6.1. In an isosceles triangle ABC, one of the angles is equal to the difference of the other two, and one of the angles is twice another. The angle bisectors of angles A, B, and C intersect the circumcircle of the triangle at points L, O, and M respectively. Find the area of triangle LOM, if the area of triangle ABC is 8. If the answer is not an integer, round it to the nearest integer.
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
Answer: 11. Solution. Let in triangle ABC the angle α be equal to the difference of angles β−γ. Since α+β+γ=180∘, then β−γ+β+γ=180∘ and therefore β=90∘. If β=90∘ is twice one of the angles α or γ, then the triangle will be isosceles, which contradicts the condition. Let for definiteness α>γ. Then β=90∘,α=60∘,γ=30∘.
Thus, the angles of triangle LOM are α1=75∘,β1=60∘,γ1=45∘.
Using the sine rule, we get the formula for the area of a triangle inscribed in a circle of radius R:S=21absinγ=21⋅2Rsinα⋅2Rsinβ⋅sinγ=2R2sinαsinβsinγ.
Therefore, SABCSLOM=2R⋅sinαsinβsinγ2R⋅sinα1sinβ1sinγ1=sin90∘sin60∘sin30∘sin75∘sin60∘sin45∘=2⋅sin75∘. Since sin75∘=sin(45∘+30∘)=46+2, we get: SABCSLOM=23+1.
Therefore, SLOM=43+4≈11.
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